This invention relates to the use of certain fatty alcohol sulfates for cleaning boreholes, drilling equipment and drill cuttings and to processes for cleaning boreholes, drilling equipment and drill cuttings.
In the drilling and development of oil and gas occurrences, cleaning steps have to be introduced at various stages to ensure problem-free drilling and production. Thus, after the actual drilling process, the borehole has to be prepared for the production of oil or gas (completion). To this end, an outer tube or casing has to be introduced and cemented in place to stabilize the borehole. The cement is passed through the casing in an aqueous liquid form, emerges at the lower end of the casing and hardens between the borehole wall and the casing. To guarantee optimal cementing, the borehole wall and the casings have to be freed from adhering residues of the drilling mud and adhering fine-particle solids. If this is not done, the layer of concrete is in danger of developing voids or channels which reduce the stability of the concrete. In addition, residues of the drilling mud and the cement together can form a gelatinous mass which prevents the cement from setting so that the stability of the cement jacket is further reduced.
After the casing has been introduced into the borehole, the actual production tube, which is smaller in diameter than the casing, is installed. In addition, a sealing fluid (or packer fluid as it is also known) is introduced between the production tube and the inner wall of the casing. Before this packer fluid is introduced, the annular space between the casing and the production tube is cleaned. In particular, all fine-particle solids still adhering to the wall of the casing or production tube have to be removed to guarantee the performance of the packer fluid.
The choice of the cleaning composition to perform the functions mentioned above is also determined by the nature of the drilling mud used. In principle, drilling muds are divided into water-based types and oil-based types. Oil-based drilling muds are mainly used today either as so-called “true oil muds”, i.e. muds which contain little if any dispersed water, or as so-called invert muds which contain between 5 and 45% by weight of water as dispersed phase, i.e. which form a w/o emulsion. In addition, there are water-based o/w emulsions which contain a heterogeneous finely disperse oil phase in a continuous aqueous phase. Petroleum products, such as mineral or diesel oils, are normally used as the oil phase. However, increasingly more stringent ecological requirements have recently led to the development of synthetic oil phases, for example containing esters of certain fatty acids. Drilling muds based on such ester oils are described, for example, in European patents 386 636, 374 671 and 374 672 and show distinctly improved behaviour compared with petroleum products in regard to their biological degradability and toxicity. Where drilling muds based on synthetic esters are used, the formation of tacky residues on metal surfaces and on the borehole wall are occasionally observed and can also lead to troublesome deposits.
In the same way as the cement used for the cementing process, the cleaning compositions are pumped downwards through the drill pipe in liquid form, emerge at the bottom of the borehole and are forced upwards through the annular space between the tube and the borehole wall. They detach residues of the drilling muds and solid particles adhering to the surfaces and remove them from the borehole. One such process is described in detail, for example, in WO 94/29570. The compositions are normally used in the form of aqueous or non-aqueous solutions or dispersions. However, they may also be added to the drilling mud in concentrated, solid or liquid form. Cleaning compositions for the functions described above may be, for example, mixtures of citric acid, pyrophosphate and potassium salts used in solid or dissolved form. These compositions are suitable both for true oil muds and for invert muds.
WO 95/17244 describes a composition for cleaning surfaces soiled with oil which contain surfactants with HLB values of at least 8 in combination with an oil. Ethoxylated sorbitan fatty acid esters are mentioned as preferred surfactants. Now, although compositions based on ethoxylated sorbitan fatty acid esters develop a favourable cleaning effect, their biological degradability and toxicity do not meet all the requirements of increasingly more stringent environmental legislation.
WO 98/19043 discloses specific soya polyol alkoxylates as highly effective cleaning agents for boreholes and drilling equipment. However, there remains a constant need to improve the environmental compatibility of cleaning compositions and, in particular, to reduce their toxicity and to improve their biodegradability while at the same time increasing their cleaning performance.
Accordingly, the problem addressed by the present invention was to provide cleaning compositions for boreholes, drilling equipment or drill cuttings which would show improved ecological compatibility, above all reduced toxicity, in relation to known compositions for at least the same cleaning performance.